CN113755161A - Quantum dot composition, light-emitting element, and method for manufacturing light-emitting element - Google Patents

Abstract

Provided are a quantum dot composition, a light emitting element, and a method for manufacturing the light emitting element. The quantum dot composition includes a quantum dot having a surface to which a ligand is bonded and a thermal decomposition auxiliary compound. The quantum dot composition may be applied to display devices and emission layers of light emitting elements, thereby improving the light emitting efficiency of the light emitting elements and display devices.

Description

Quantum dot composition, light-emitting element, and method for manufacturing light-emitting element

This application claims priority and benefit from korean patent application No. 10-2020-0066732, filed on 6/2/2020, which is hereby incorporated by reference in its entirety.

Technical Field

The present disclosure herein relates to a quantum dot composition, a light emitting element including an emission layer formed of the quantum dot composition, and a method for manufacturing the light emitting element.

Background

Various types of display devices for multimedia devices are being developed (such as televisions, mobile phones, tablet computers, navigation systems, and/or game consoles). In such a display device, a so-called self-light emitting display element is used in which display is completed by causing a light emitting material containing an organic compound to emit light.

In addition, efforts are being made to develop a light emitting element using quantum dots as a light emitting material to enhance color reproducibility of a display device, and it is required to improve light emitting efficiency and service life of the light emitting element using quantum dots.

Disclosure of Invention

One or more aspects of embodiments according to the present disclosure relate to a quantum dot composition having improved dispersibility.

One or more aspects according to embodiments of the present disclosure also relate to a light emitting element having improved luminous efficiency by including an emission layer having a plurality of quantum dots that are uniformly distributed and close to each other.

One or more aspects according to embodiments of the present disclosure also relate to a method for manufacturing a light emitting element including forming an emission layer having improved luminous efficiency by removing ligands bound to quantum dots.

According to an embodiment of the present disclosure, a quantum dot composition includes a quantum dot having a surface to which a ligand is bound and a thermal decomposition assisting compound.

The ligand may include a head portion bound to the surface of the quantum dot and a tail portion comprising at least one free radical reactive group.

The free radical reactive group may be a carbonyl group, an ester group, an ether group, a peroxy group, an azo group, a carbamate group, a thiocarbamate group, a carbonate group, or a xanthate group.

The ligand may be a monodentate ligand or a bidentate ligand.

The head may include a thiol group, a hydroxyl group, a phosphino group, a fluorenyl group, an amine group, or a carboxylic acid group.

The head may also include an alkyl group having 1 to 6 carbon atoms.

The tail may be represented by any one selected from the followingformulas 1 to 6.

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5

Formula 6

In theabove formulas 1 to 6, R₂May be an alkyl group having 2 to 20 carbon atoms, m may be an integer of 1 to 5, and "" may indicate a position of attachment to the head.

The thermal decomposition auxiliary compound may be an azo compound.

The azo compound may be represented by formula 7 below.

Formula 7

Ra-N＝N-Rb

In formula 7 above, Ra and Rb may each independently be an alkyl group having 2 to 20 carbon atoms.

The quantum dots having the ligands bound to the surfaces thereof may be included in an amount of about 0.5 wt% to about 10 wt% with respect to the total amount of the quantum dot composition.

The thermal decomposition auxiliary compound may be included in an amount of about 0.01 wt% to about 1 wt% with respect to the total amount of the quantum dot composition.

The quantum dot composition may further include an organic solvent, and the quantum dots may be dispersed in the organic solvent.

The quantum dots may be semiconductor nanocrystals comprising a core and a shell surrounding the core.

According to an embodiment of the present disclosure, a method for manufacturing a light emitting element includes the steps of: forming a hole transport region on the first electrode; forming an emission layer on the hole transport region; forming an electron transport region on the emission layer; and forming a second electrode on the electron transport region, wherein the forming of the emission layer includes: dispersing a quantum dot having a surface to which a ligand is bonded and a thermal decomposition auxiliary compound in an organic solvent to prepare a quantum dot composition; applying a quantum dot composition on the hole transport region to form a preliminary emission layer; and heating the preliminary emission layer.

The thermal decomposition auxiliary compound may be represented by formula 7, and may be included in an amount of about 0.01 wt% to about 1 wt% with respect to the total amount of the quantum dot composition.

Formula 7

Ra-N ═ N-Rb in formula 7 above, Ra and Rb may each independently be an alkyl group having 2 to 20 carbon atoms.

The step of heating the preliminary emissive layer may be performed by heating the preliminary emissive layer at about 120 ℃ to about 180 ℃ for 20 minutes or more.

The quantum dot may include a core and a shell surrounding the core, and the ligand may include a hydrophilic group and a radical reactive group bound to a surface of the quantum dot.

The hydrophilic group may be a thiol group, dithio group, phosphino group, catechol group, amine group, or carboxylic acid group.

In an embodiment of the present disclosure, a light emitting element includes: a first electrode; a hole transport region on the first electrode; an emission layer on the hole transport region; an electron transport region on the emission layer; and a second electrode on the electron transport region, wherein the emission layer includes quantum dots having a surface to which hydrophilic groups are bonded.

The emissive layer may also include a residue comprising a free radical reactive group.

Drawings

The accompanying drawings are included to provide a further understanding of the disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the disclosure and together with the description serve to explain the principles of the disclosure. In the drawings:

fig. 1 is a perspective view of an electronic apparatus of an embodiment;

fig. 2 is an exploded perspective view of the electronic apparatus of the embodiment;

fig. 3 is a sectional view of the display device according to the embodiment corresponding to a line I-I' of fig. 2;

fig. 4 is a sectional view of a light emitting element of the embodiment;

fig. 5 is a schematic diagram of a quantum dot having a ligand bound to its surface of an embodiment;

fig. 6 is a cross-sectional view illustrating a quantum dot composition according to an embodiment;

fig. 7 is a flowchart illustrating a method for manufacturing a light emitting element according to an embodiment;

fig. 8 is a cross-sectional view schematically illustrating one or more actions of forming a preliminary emission layer according to an embodiment;

fig. 9 is a cross-sectional view schematically illustrating one or more acts of forming an emission layer according to an embodiment;

FIG. 10 is a cross-sectional view of an emissive layer according to an embodiment;

fig. 11 is a plan view of a display device according to an embodiment;

fig. 12 is a sectional view of the display device according to the embodiment corresponding to a line II-II' of fig. 11; and

fig. 13 is a sectional view of a display device according to an embodiment.

Detailed Description

The disclosure may be modified in many alternative forms, and specific embodiments will therefore be illustrated in the drawings and described in more detail. It should be understood, however, that there is no intention to limit the disclosure to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

In this specification, when an element (or a region, layer, portion, or the like) is referred to as being "on," "connected to" or "coupled to" another element, it means that the element may be directly on, connected or coupled to the other element, or a third element may be disposed therebetween.

On the other hand, in the present disclosure, the term "directly disposed" means that no layer, film, region, and/or plate or the like is added between a part and another part of the layer, film, region, and/or plate or the like. For example, "directly disposed" may refer to being disposed without an additional member such as an adhesive member between two layers or two members.

Like reference numerals refer to like elements. In addition, in the drawings, the thickness, proportion, and size of elements are exaggerated for effective description of technical contents.

The term "and/or" includes all combinations that the associated configuration (or arrangement) may define one or more of them.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments of the present disclosure. Terms in the singular may include the plural unless the context clearly dictates otherwise.

Additionally, terms such as "below … …," "below," "above … …," and/or "upper" are used to describe the relationship of the configurations shown in the figures. Terms are used as relative concepts and are described with reference to directions indicated in the drawings.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

It will be understood that the terms "comprises" and "comprising," or "having" are intended to specify the presence of stated features, integers, steps, operations, elements, components, or combinations thereof in the disclosure, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or groups thereof.

Hereinafter, a quantum dot composition, a light emitting element, and a display device including the light emitting element according to embodiments of the present disclosure will be described with reference to the accompanying drawings.

Fig. 1 is a perspective view of an electronic apparatus EA of the embodiment. Fig. 2 is an exploded perspective view of the electronic apparatus EA of the embodiment. Fig. 3 is a cross-sectional view of the display device DD according to the embodiment corresponding to the line I-I' of fig. 2. Fig. 4 is a sectional view of the display device DD of the embodiment.

In an embodiment, the electronic device EA may be a large electronic device such as a television, a monitor and/or an outdoor billboard. Additionally, the electronic device EA may be a small and/or medium sized electronic device such as a personal computer, a laptop computer, a personal digital terminal, a car navigation unit, a game console, a smart phone, a tablet computer, and/or a camera. However, these are presented by way of example only, and thus other suitable electronic devices may be used without departing from this disclosure. In the present embodiment, a smartphone is exemplarily shown as the electronic device EA.

The electronic apparatus EA may include a display device DD and a case HAU. The display device DD may display the image IM through the display surface IS, and the user may view the image IM provided through the transmissive area TA corresponding to the front surface FS of the electronic apparatus EA. The image IM may include a still image as well as a moving image. Fig. 1 shows that the front surface FS is parallel to a plane defined by the first direction DR1 and a second direction DR2 intersecting thefirst direction DR 1. However, this is presented only as an example, in another embodiment the front surface FS of the electronic device EA may have a curved shape.

Among the normal directions of the front surface FS of the electronic apparatus EA (i.e., the thickness direction of the electronic apparatus EA), the direction along which the image IM is displayed is indicated by athird direction DR 3. The front (or upper) and rear (or lower) surfaces of each member may be defined by athird direction DR 3.

The fourth direction DR4 (see fig. 11) may be a direction between the first direction DR1 and thesecond direction DR 2. The fourth direction DR4 may lie on a plane parallel to a plane defined by the first direction DR1 and thesecond direction DR 2. The directions indicated by the first direction DR1, the second direction DR2, the third direction DR3 and the fourth direction DR4 are relative concepts, and thus may be changed to other directions.

According to an embodiment, the electronic apparatus EA may include a foldable display device having a folding area and a non-folding area, or a curved (e.g., bendable) display device having at least one curved portion.

The electronic apparatus EA may include a display device DD and a case HAU. In the electronic apparatus EA, the front surface FS may correspond to a front surface of the display device DD, and may also correspond to a front surface of the window WP. Therefore, the front surface of the electronic apparatus EA, the front surface of the display device DD, and the front surface of the window WP will be referred to using reference numeral FS.

The case HAU may accommodate the display device DD. The case HAU may be disposed to cover the display device DD such that an upper surface as a display surface IS of the display device DD IS exposed. The case HAU may cover the side and bottom surfaces of the display device DD and expose the entire (e.g., entire) upper surface. However, embodiments of the present disclosure are not limited thereto, and the case HAU may cover a portion of the upper surface and the side and bottom surfaces of the display device DD.

In the electronic device EA of the embodiment, the window WP may include an optically transparent insulating material. The window WP may include a transmission area TA and a bezel area BZA. The front surface FS of the window WP including the transmissive area TA and the bezel area BZA corresponds to the front surface FS of the electronic device EA.

In fig. 1 and 2, the transmissive area TA is shown as a rectangular shape having rounded vertices. However, this is exemplarily shown, and the transmissive area TA may have various suitable shapes, and is not limited to any one embodiment.

The transmissive area TA may be an optically transparent area. The bezel area BZA may be an area having a relatively lower transmittance than that of the transmissive area TA. The bezel area BZA may have a set or predetermined color. The bezel area BZA may be adjacent to and surround the transmission area TA. The bezel area BZA may define the shape of the transmission area TA. However, embodiments of the present disclosure are not limited to the illustrated embodiments, the bezel area BZA may be disposed adjacent to only one side of the transmission area TA, and a portion of the bezel area BZA may be omitted.

The display device DD may be disposed below the window WP. In this specification, "under … …" may indicate a direction opposite to a direction along which the display device DD provides (e.g., displays) the image IM.

In an embodiment, the display device DD may be substantially configured to generate the image IM. The image IM generated in the display device DD IS displayed on the display surface IS and IS viewed from the outside by the user through the transmissive area TA. The display device DD includes a display area DA and a non-display area NDA. The display area DA may be an area activated according to an electrical signal. The non-display area NDA may be an area covered by the bezel area BZA. The non-display area NDA is adjacent to the display area DA. The non-display area NDA may surround the display area DA.

Referring to fig. 3, the display device DD may include a display panel DP and an optical control layer PP disposed on the display panel DP. The display panel DP may include a display element layer DP-EL. The display element layer DP-EL includes a light emitting element ED (see fig. 4).

The optical control layer PP may be disposed on the display panel DP to control reflected light from the display panel DP due to external light. The light control layer PP may comprise, for example, a polarizing layer and/or a color filter layer.

In the display device DD of the embodiment, the display panel DP may be a light emitting display panel. For example, the display panel DP may be a quantum dot light emitting display panel including quantum dot light emitting elements. However, embodiments of the present disclosure are not limited thereto.

The display panel DP may include a base substrate BS, a circuit layer DP-CL disposed on the base substrate BS, and a display element layer DP-EL disposed on the circuit layer DP-CL.

The base substrate BS may be a member that provides a base surface on which the display element layer DP-EL is provided. The base substrate BS may be a glass substrate, a metal substrate, a plastic substrate, or the like. However, embodiments of the present disclosure are not limited thereto, and the base substrate BS may be an inorganic layer, an organic layer, or a composite material layer. The base substrate BS may be a flexible substrate that can be easily bent or folded.

In an embodiment, the circuit layer DP-CL may be disposed on the base substrate BS, and the circuit layer DP-CL may include a plurality of transistors. The transistors may each include a control electrode, an input electrode, and an output electrode. For example, the circuit layer DP-CL may include a switching transistor and a driving transistor to drive the light emitting element ED of the display element layer DP-EL.

Fig. 4 is a cross-sectional view illustrating a light emitting element ED according to an embodiment, and referring to fig. 4, the light emitting element ED according to the embodiment includes a first electrode EL1, a second electrode EL2 facing the first electrode EL1, and a plurality of functional layers disposed between the first electrode EL1 and the second electrode EL2 and including an emission layer EML.

The plurality of functional layers may include a hole transport region HTR disposed between the first electrode EL1 and the emission layer EML and an electron transport region ETR disposed between the emission layer EML and thesecond electrode EL 2. According to an embodiment, a cap layer may be further disposed on thesecond electrode EL 2.

Both the hole transport region HTR and the electron transport region ETR may include a plurality of sub-functional layers. For example, the hole transport region HTR may include a hole injection layer HIL and a hole transport layer HTL as sub-functional layers, and the electron transport region ETR may include an electron injection layer EIL and an electron transport layer ETL as sub-functional layers. However, embodiments of the present disclosure are not limited thereto, and the hole transport region HTR may further include an electron blocking layer as a sub-functional layer, and the electron transport region ETR may further include a hole blocking layer as a sub-functional layer.

In the light emitting element ED according to the embodiment, the first electrode EL1 has conductivity. The first electrode EL1 may be formed of a metal alloy or a conductive compound. The first electrode EL1 may be an anode. The first electrode EL1 may be a pixel electrode.

In the light emitting element ED according to the embodiment, the first electrode EL1 may be a reflective electrode. However, embodiments of the present disclosure are not limited thereto. For example, the first electrode EL1 may be a transmissive electrode or a transflective electrode. When the first electrode EL1 is a transflective or reflective electrode, the first electrode EL1 can include Ag, Mg, Cu, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF/Al, Mo, Ti, compounds thereof, or mixtures thereof (e.g., a mixture of Ag and Mg). In some embodiments, the first electrode EL1 may have a multilayer structure including a reflective film or a transflective film formed of the above-described materials as examples, and a transparent conductive film formed of Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Tin Zinc Oxide (ITZO), or the like. For example, the first electrode EL1 may be a multi-layered metal film, and may have a stacked structure of metal films of ITO/Ag/ITO.

The hole transport region HTR is disposed on thefirst electrode EL 1. The hole transport region HTR may include a hole injection layer HIL, a hole transport layer HTL, and the like. In some embodiments, the hole transport region HTR may further include at least one of a hole buffer layer and an electron blocking layer in addition to the hole injection layer HIL and the hole transport layer HTL. The hole buffer layer may compensate for an optical resonance distance according to a wavelength of light emitted from the emission layer EML, and thus may increase light emission efficiency. A material that can be included in the hole transport region HTR can be used as a material included in the hole buffer layer. The electron blocking layer is a layer for preventing or substantially preventing electrons from being injected from the electron transport region ETR to the hole transport region HTR.

The hole transport region HTR may have a single layer formed of a single material, a single layer formed of a plurality of different materials, or a multilayer structure including a plurality of layers formed of a plurality of different materials. For example, the hole transport region HTR may have a single-layer structure formed of a plurality of different materials, or a structure in which a hole injection layer HIL/hole transport layer HTL, a hole injection layer HIL/hole transport layer HTL/hole buffer layer, a hole injection layer HIL/hole buffer layer, a hole transport layer HTL/hole buffer layer, or a hole injection layer HIL/hole transport layer HTL/electron blocking layer is stacked from the first electrode EL1 in the order stated accordingly, but the embodiments of the present disclosure are not limited thereto.

The hole transport region HTR may be formed using various suitable methods such as a vacuum deposition method, a spin coating method, a casting method, a langmuir-blodgett (LB) method, an inkjet printing method, a laser printing method, and/or a Laser Induced Thermal Imaging (LITI) method.

The hole injection layer HIL may include, for example, phthalocyanine compounds such as copper phthalocyanine, N '-diphenyl-N, N' -bis [ 4-di (m-tolyl) -amino-phenyl ] -biphenyl-4, 4 '-diamine (DNTPD), 4' ″ - [ tris (3-methylphenyl) phenylamino ] triphenylamine (m-MTDATA), 4 '″ -tris (N, N-diphenylamino) triphenylamine (TDATA), 4' ″ -tris (N- (2-naphthyl) -N-phenylamino) -triphenylamine (2-TNATA), poly (3, 4-ethylenedioxythiophene)/poly (4-styrenesulfonate) (PEDOT/PSS), polyaniline/dodecylbenzenesulfonic acid (PANI/DBSA), Polyaniline/camphorsulfonic acid (PANI/CSA), polyaniline/poly (4-styrenesulfonate) (PANI/PSS), N ' -di (naphthalene-1-yl) -N, N ' -diphenyl-benzidine (NPB), triphenylamine-containing polyetherketone (TPAPEK), 4-isopropyl-4 ' -methyldiphenyliodonium tetrakis (pentafluorophenyl) borate, dipyrazino [2,3-f: 2', 3 ' -h ] quinoxaline-2, 3,6,7,10, 11-hexanenitrile (HAT-CN), and the like.

The hole transport layer HTL may comprise any suitable material (e.g., common materials known in the art). The hole transport layer HTL may include, for example, carbazole-based derivatives such as N-phenylcarbazole and/or polyvinylcarbazole, fluorene-based derivatives, N '-bis (3-methylphenyl) -N, N' -diphenyl- [1,1 '-biphenyl ] -4, 4' -diamine (TPD), triphenylamine-based derivatives such as 4,4 '-tris (N-carbazolyl) triphenylamine (TCTA), N' -bis (naphthalen-1-yl) -N, N '-diphenyl-benzidine (NPB), 4' -cyclohexylidene bis [ N, N-bis (4-methylphenyl) aniline ] (TAPC), 4 '-bis [ N, N' - (3-tolyl) amino ] -3, 3' -dimethylbiphenyl (HMTPD), 1, 3-bis (N-carbazolyl) benzene (mCP), and the like.

The hole transport region HTR may have a thickness of about 5nm to about 1,500nm (e.g., about 10nm to about 500 nm). The hole injection layer HIL may have a thickness of, for example, about 3nm to about 100nm, and the hole transport layer HTL may have a thickness of about 3nm to about 100 nm. For example, the electron blocking layer may have a thickness of about 1nm to about 100 nm. When the thicknesses of the hole transport region HTR, the hole injection layer HIL, the hole transport layer HTL, and the electron blocking layer satisfy the above-described ranges, desired (e.g., satisfactory) electron injection properties may be obtained without significantly increasing the driving voltage.

The emission layer EML is disposed on the hole transport region HTR. The emission layer EML comprises quantum dots MQD combined with a plurality of hydrophilic groups. The quantum dot MQD having the hydrophilic group bonded thereto has a functional group as a hydrophilic group bonded to the surface of the quantum dot, and may have modified surface properties. Hereinafter, the quantum dot MQD to which the hydrophilic group is bonded is referred to as a surface-modified quantum dot MQD. The hydrophilic group bound to the quantum dot may be a head of a ligand, which will be described in more detail later.

The surface-modified quantum dots MQD included in the emission layer EML may be stacked to form a layer. In fig. 4, for example, the surface-modified quantum dots MQD having a circular cross-section are arranged to form two layers, but embodiments of the present disclosure are not limited thereto. For example, the arrangement of the surface-modified quantum dots MQD may vary according to the thickness of the emission layer EML, the shape of the quantum dots QD (see fig. 5) included in the emission layer EML, and the average diameter of the quantum dots QD. In some embodiments, in the emission layer EML, the surface modified quantum dots MQD may be aligned to be adjacent to each other to form a single layer, or may be aligned to form multiple layers such as two or three layers. The quantum dot composition and the surface modified quantum dot MQD will be described in more detail later.

In some embodiments, in the light emitting element ED, the emission layer EML may include a host and a dopant. In an embodiment, the emission layer EML may comprise surface modified quantum dots MQD as dopant material. In addition, in an embodiment, the emission layer EML may further include a host material.

In some embodiments, in the light emitting element ED, the emission layer EML may emit fluorescence. For example, surface-modified quantum dots, MQDs, can be used as fluorescent dopant materials.

In the light emitting element ED of the embodiment, the electron transport region ETR is disposed on the emission layer EML. The electron transport region ETR may include (e.g., be selected from) at least one of a hole blocking layer, an electron transport layer ETL, and an electron injection layer EIL, but the embodiments of the present disclosure are not limited thereto.

The electron transport region ETR may have a single layer formed of a single material (e.g., composed of a single material), a single layer formed of a plurality of different materials, or a multi-layer structure including a plurality of layers formed of a plurality of different materials.

For example, the electron transport region ETR may have a single-layer structure of the electron injection layer EIL or the electron transport layer ETL, or may have a single-layer structure formed of an electron injection material and an electron transport material. In addition, the electron transport region ETR may have a single-layer structure formed of a plurality of different materials, or may have a structure in which an electron transport layer ETL/an electron injection layer EIL or a hole blocking layer/an electron transport layer ETL/an electron injection layer EIL are stacked from an emission layer EML in the order stated, respectively, but the embodiments of the present disclosure are not limited thereto. The thickness of the electron transport region ETR may be, for example, from about 20nm to about 150 nm.

The electron transport region ETR may be formed using various suitable methods such as a vacuum deposition method, a spin coating method, a casting method, a langmuir-blodgett (LB) method, an inkjet printing method, a Laser Induced Thermal Imaging (LITI) method, and the like.

When the electron transport region ETR includes the electron transport layer ETL, the electron transport layer ETL may include an anthracene compound. However, embodiments of the present disclosure are not limited thereto, and the electron transport layer ETL may include, for example, tris (8-hydroxyquinoline) aluminum (Alq)₃) 1,3, 5-tris [ (3-pyridyl) -phen-3-yl]Benzene, 2,4, 6-tris (3' - (pyridin-3-yl) biphenyl-3-yl) -1,3, 5-triazine, 2- (4- (N-phenylbenzimidazol-1-yl) phenyl) -9, 10-dinaphthylanthracene, 1,3, 5-tris (1-phenyl-1H-benzo [ d ] b]Imidazol-2-yl) benzene (TPBi), 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP), 4, 7-diphenyl-1, 10-phenanthroline (Bphen), 3- (4-biphenyl) -4-phenyl-5-tert-butylphenyl-1, 2, 4-Triazole (TAZ), 4- (naphthalen-1-yl) -3, 5-diphenyl-4H-1, 2, 4-triazole (NTAZ), 2- (4-biphenyl) -5- (4-tert-butylphenyl) -1,3, 4-oxadiazole (tBu-PBD), bis (2-methyl-8-hydroxyquinoline-N1, O8) - (1, 1' -biphenyl-4-hydroxy) aluminum (BAlq), bis (benzoquinoline-10-hydroxy) beryllium (Bebq)₂) 9, 10-di (naphthalen-2-yl) Anthracene (ADN), or mixtures thereof. The thickness of the electron transport layer ETL may be from about 10nm to about 100nm, and may be, for example, from about 15nm to about 50 nm. When the thickness of the electron transport layer ETL satisfies the above range, a desired (e.g., satisfactory) electron transport property can be obtained without significantly increasingA driving voltage.

When the electron transport region ETR includes the electron injection layer EIL, the electron injection layer EIL may include a halogenated metal (such as LiF, NaCl, CsF, RbCl, and/or RbI), a lanthanide metal (such as Yb), a metal oxide (such as Li)₂O and/or BaO) or lithium quinolinolate (LiQ), although embodiments of the present disclosure are not so limited. The electron injection layer EIL may also be formed of a mixed material of an electron injection material and an insulating organic metal salt. The organometallic salts may include, for example, metal acetates, metal benzoates, metal acetoacetates, metal acetylacetonates, and/or metal stearates. The thickness of the electron injection layer EIL may be about 0.1nm to about 10nm, for example, about 0.3nm to about 9 nm. When the thickness of the electron injection layer EIL satisfies the above range, a satisfactory electron injection property can be obtained without significantly increasing the driving voltage.

The electron transport region ETR may include a hole blocking layer as described above. The hole blocking layer may include, for example, at least one of 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP) and 4, 7-diphenyl-1, 10-phenanthroline (Bphen), but embodiments of the present disclosure are not limited thereto.

The second electrode EL2 is disposed on the electron transport region ETR. The second electrode EL2 may be a common electrode and/or a cathode. The second electrode EL2 may be a transmissive electrode, a transflective electrode, or a reflective electrode. When the second electrode EL2 is a transmissive electrode, the second electrode EL2 may be formed of a transparent metal oxide, for example, Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Tin Zinc Oxide (ITZO), or the like.

When the second electrode EL2 is a transflective or reflective electrode, the second electrode EL2 may include Ag, Mg, Cu, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, LiF/Al, Mo, Ti, Yb, compounds thereof (e.g., AgYb, AgMg, MgAg compounds, etc. according to the content) or mixtures thereof (e.g., a mixture of Ag and Mg, a mixture of Ag and Yb, etc.). For example, the second electrode EL2 may include AgMg, AgYb, or MgAg. In some embodiments, the second electrode EL2 may have a multilayer structure including a reflective film or a transflective film formed of any one of the above materials and a transparent conductive film formed of Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), zinc oxide (ZnO), Indium Tin Zinc Oxide (ITZO), or the like.

In some embodiments, the second electrode EL2 may be connected to an auxiliary electrode. When the second electrode EL2 is connected to the auxiliary electrode, the resistance of the second electrode EL2 may be reduced.

Fig. 5 is a schematic diagram of a quantum dot QD and a ligand LD included in the quantum dot composition of the embodiment. Fig. 6 is a view illustrating a quantum dot composition QCP according to an embodiment.

The quantum dot composition QCP according to the embodiment includes quantum dots QD, a ligand LD bound to the surface of the quantum dots QD, and a thermal decomposition auxiliary compound RC as a reaction additive. The thermal decomposition auxiliary compound RC may be, for example, an azo compound. Quantum dots QD may have ligands LD bound to their surface. For example, the quantum dot QD may include a core CR and a shell SL, and the ligand LD may be bound to the shell SL.

The quantum dot QD has a ligand LD bound to its surface to maintain charge injection properties while improving dispersibility and capping properties. Fig. 5 schematically shows a quantum dot QD with a ligand LD bound to its surface. When the emission layer is formed, the ligand LD bound to the quantum dot QD is partially removed, thereby reducing or preventing the deterioration of charge injection properties.

The quantum dots QD of embodiments may be semiconductor nanocrystals that may be selected from group II-VI compounds, group III-V compounds, group IV-VI compounds, group IV elements, group IV compounds, group I-III-VI compounds, and combinations thereof.

The II-VI compound may be selected from: a binary compound selected from the group consisting of CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, and mixtures thereof; a ternary compound selected from the group consisting of CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, and mixtures thereof; and a quaternary compound selected from the group consisting of CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe and mixtures thereof.

The group III-VI compounds may include: binary compounds, such as In₂S₃And/or In₂Se₃(ii) a Ternary compounds, such as InGaS₃And/or InGaSe₃(ii) a Or any combination thereof.

The III-V compound may be selected from: a binary compound selected from the group consisting of GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, and mixtures thereof; a ternary compound selected from the group consisting of GaNP, GaNAs, GaNSb, GaAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InGaP, InAlP, InNP, InNAs, InNSb, InPAs, InPSb, and mixtures thereof; and a quaternary compound selected from the group consisting of GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, and mixtures thereof. The III-V compounds may also include group II metals (e.g., InZnP, etc.).

The group IV-VI compounds may be selected from: a binary compound selected from the group consisting of SnS, SnSe, SnTe, PbS, PbSe, PbTe and mixtures thereof; a ternary compound selected from the group consisting of SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe and mixtures thereof; and a quaternary compound selected from the group consisting of SnPbSSe, SnPbSeTe, SnPbSTe, and mixtures thereof. The group IV element may be selected from Si, Ge and mixtures thereof. The group IV compound may be a binary compound selected from SiC, SiGe and mixtures thereof.

The I-III-VI compounds may include ternary compounds such as AgInS, AgInS₂、CuInS、CuInS₂、CuGaO₂、AgGaO₂、AgAlO₂Or any combination thereof.

In some embodiments, the binary, ternary, or quaternary compounds may be present in the particle in a uniform concentration distribution, or may be present in the same particle in a partially different (e.g., non-uniform) concentration distribution. That is, the elements of the binary compound, the ternary compound, or the quaternary compound may be present in the particles in a uniform concentration distribution, or may be present in the particles in a non-uniform concentration distribution. In some embodiments, there may be a core/shell structure in which one quantum dot surrounds another quantum dot. The interface between the core and the shell may have a concentration gradient in which the concentration of the element present in the shell becomes lower (decreases) toward the center.

In some embodiments, the quantum dots QD may have a core/shell structure including a core CR having nanocrystals (e.g., formed of nanocrystals) described above and a shell SL surrounding the core CR. The shell SL of the quantum dot QD having a core/shell structure may be used as a protective layer to reduce or prevent chemical deformation of the core CR to maintain semiconductor properties, and/or as a charging layer to impart electrophoretic properties to the quantum dot QD. The shell SL may be a single layer or a multilayer. The interface between the core CR and the shell SL may have a concentration gradient in which the concentration of the element present in the shell SL becomes lower (decreases) toward the center. Examples of the shell SL of the quantum dot QD having a core-shell structure may be a metal oxide, a non-metal oxide, a semiconductor compound, or a combination thereof.

For example, the metal oxide or metalloid oxide can be a binary compound (such as SiO)₂、Al₂O₃、TiO₂、ZnO、MnO、Mn₂O₃、Mn₃O₄、CuO、FeO、Fe₂O₃、Fe₃O₄、CoO、Co₃O₄And/or NiO) or ternary compounds (such as MgAl₂O₄、CoFe₂O₄、NiFe₂O₄And/or CoMn₂O₄) However, embodiments of the present disclosure are not limited thereto.

In some embodiments, the semiconductor compound may be, for example, CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnSeS, ZnTeS, GaAs, GaP, GaSb, HgS, HgSe, HgTe, InAs, InP, InGaP, InSb, AlAs, AlP, AlSb, etc., although embodiments of the present disclosure are not limited thereto.

The quantum dot QDs may have a full width at half maximum (FWHM) of a light emitting wavelength spectrum of about 45nm or less (e.g., about 40nm or less or about 30nm or less), and within the above range, color purity and/or color reproducibility may be enhanced. In addition, light emitted by such quantum dots QD is emitted in all directions, and thus a wide viewing angle may be improved.

The form of the quantum dot QD is not particularly limited as long as it is a suitable form (e.g., a form generally used in the related art), and for example, quantum dots in the form of nanoparticles, nanotubes, nanowires, nanofibers, nanosheets, etc., in a spherical, pyramidal, multi-arm, and/or cubic shape, may be used.

The quantum dot QD may control the color of emitted light according to its particle diameter, and thus, the quantum dot QD may have various suitable emission colors, such as blue, red, green, and the like. The smaller the particle size of the quantum dot QD, the shorter the wavelength region of light that can be emitted. For example, in quantum dots QD having the same core, the particle size of a quantum dot emitting green light may be smaller than that of a quantum dot emitting red light. In some embodiments, in quantum dots QD having the same core, the particle size of a quantum dot emitting blue light may be smaller than the particle size of a quantum dot emitting green light. However, embodiments of the present disclosure are not limited thereto, and even in the quantum dot QD having the same core, the particle diameter may be adjusted according to the thickness and material of the shell.

In some embodiments, quantum dots QD providing (or having) different luminescent colors may have different core materials when they are to provide (or have) one of various suitable luminescent colors (such as blue, red, green, etc.).

As described above, the quantum dot QD may include a core CR and a shell SL surrounding the core CR. However, embodiments of the present disclosure are not limited thereto, and the quantum dot QDs may have a single-layer structure or may have a plurality of shells.

The ligand LD includes a head HD bound to the surface of the quantum dot QD and a tail TL exposed to the outside, and may be removed by a radical reaction.

The head HD of the ligand LD, which is not removed even after the radical reaction, is bound to the surface of the quantum dot QD to form a surface-modified quantum dot MQD. For example, equivalent quantum dot QDs includeCore CR and shell SL, head HD may be bonded to shell SL. For example, when head HD includes a thiol group and shell SL includes a metal ion Zn (e.g., Zn)²⁺) When the thiol group of the head HD binds to Zn to allow the ligand LD to bind to the quantum dot QD.

The head HD may include functional groups bound (e.g., attached) to the surface of the quantum dots QD. The functional group bonded (e.g., attached) to the surface of the quantum dot QD may be a hydrophilic group, and may include, for example, a thiol group, a hydroxyl group, a phosphine group, a fluorenyl group, an amine group, and/or a carboxylic acid group. However, embodiments of the present disclosure are not limited thereto.

When the head HD comprises a single functional group bound (e.g., linked) to the surface of the quantum dot QD, the ligand LD may be a monodentate ligand. When the head HD comprises two functional groups bound (e.g., linked) to the surface of the quantum dot QD, the ligand LD may be a bidentate ligand. The head HD may include functional groups bound (e.g., attached) to the surface of the shell SL of the quantum dot QD.

In some embodiments, the head HD may also include an alkyl group having 1 to 6 carbon atoms. The head HD further includes an alkyl group having 1 to 6 carbon atoms, or, for example, 1 to 4 carbon atoms, to ensure stability to the quantum dots QD, but may not inhibit electron injection.

The tail TL of the ligand LD is the part removed in the manufacture of the emission layer EML and comprises at least one radical reactive group RG. The radical-reactive group RG is not particularly limited as long as it is a functional group capable of reacting with the thermal decomposition auxiliary compound RC. For example, the free radical reactive group RG may be a carbonyl group, an ester group, an ether group, a peroxy group, an azo group, a carbamate group, a thiocarbamate group, a carbonate group or a xanthate group.

The tail TL of the ligand LD may also include an alkyl group having 2 to 20 carbon atoms. The tail TL also includes an alkyl group to control the length of the ligand LD, thereby performing the function of controlling the dispersibility of the quantum dot QD in the quantum dot composition QCP. When the number of carbon atoms of the alkyl group of the tail TL is less than 2, the distance between the quantum dots QD may be too close, and when the number of carbon atoms is greater than 20, the distance between the quantum dots QD may be too far.

In an embodiment, the tail TL may be represented by any one selected from the followingformulas 1 to 6.

Formula 1

Formula 2

Formula 3

Formula 4

Formula 5

Formula 6

In theabove formulas 1 to 6, R₂Is a substituted or unsubstituted alkyl group having 2 to 20 carbon atoms, and m is an integer of 1 to 5.

"Tio-" in this specification indicates a position to be bonded. Informulas 1 to 6, ". sup. -" indicates the position of attachment to the head HD.

In order to effectively disperse the quantum dots QD in the quantum dot composition QCP, the quantum dots QD having the ligand LD bound to the surface thereof may be included in an amount of about 0.5 wt% or more (or about 1 wt% or more) and about 10 wt% or less (or about 5 wt% or less) relative to the total amount of the quantum dot composition QCP.

The quantum dot composition QCP according to the embodiment comprises a thermal decomposition assisting compound RC. The thermal decomposition auxiliary compound RC is not particularly limited as long as it is a compound capable of performing a radical removal reaction of the ligand LD (or a part of the ligand LD), and for example, the thermal decomposition auxiliary compound RC may be an azo compound. The quantum dot composition QCP includes the azo compound RC, and thus can effectively perform a removal reaction of the ligand LD that is performed later (e.g., performed when the emission layer EML is formed). The azo compound RC may be represented by formula 7 below.

Formula 7

Ra-N＝N-Rb

In the above-mentioned formula 7, the,

ra and Rb are each independently a substituted or unsubstituted alkyl group having 2 to 20 carbon atoms.

The azo compound RC may be used alone or in combination of two or more. The azo compound RC may be included in an amount of about 0.01 wt% or more (or about 0.03 wt% or more) and about 1 wt% or less (or about 0.7 wt% or less) with respect to the total amount of the quantum dot composition QCP to effectively perform and accelerate the reaction.

The quantum dot composition QCP may also comprise an organic solvent SV. For example, the organic solvent SV may include hexane, octane, toluene, chloroform, dimethyl sulfoxide, dimethylformamide, decane, dodecane, hexadecene, cyclohexylbenzene, tetrahydronaphthalene, ethylnaphthalene, ethylbiphenyl, isopropylnaphthalene, diisopropylnaphthalene, diisopropylbiphenyl, xylene, isopropylbenzene, pentylbenzene, diisopropylbenzene, decahydronaphthalene, phenylnaphthalene, cyclohexyldecahydronaphthalene, decylbenzene, dodecylbenzene, octylbenzene, cyclohexane, cyclopentane, cycloheptane and the like. However, embodiments of the present disclosure are not limited thereto.

Fig. 7 is a flowchart illustrating a method for manufacturing a light emitting element according to an embodiment. Fig. 8 and 9 each schematically illustrate one or more actions of a method for manufacturing a light emitting element according to an embodiment. Fig. 10 is a cross-sectional view illustrating an emission layer EML manufactured according to an embodiment.

The method for manufacturing a light emitting element includes: the method includes forming a hole transporting region on a first electrode, forming an emission layer on the hole transporting region, forming an electron transporting region on the emission layer, and forming a second electrode on the electron transporting region.

Referring to fig. 7, forming an emission layer of a light emitting element according to an embodiment includes preparing a quantum dot composition (S100), providing a preliminary emission layer (S200), and providing heat to form the emission layer (or heating the preliminary emission layer to form the emission layer) (S300).

In preparing the quantum dot composition (S100), a quantum dot (or a plurality of quantum dots) QD having a ligand LD bound to its surface and a thermal decomposition auxiliary compound RC are dispersed in an organic solvent SV. The quantum dot QD may have a ligand LD bound to its surface to improve dispersibility in an organic solvent SV.

Fig. 8 schematically shows an act of providing a preliminary emission layer in a method for manufacturing a light emitting element according to an embodiment (S200). Providing a preliminary emission layer (S200) is performed by applying the quantum dot composition QCP on the hole transport region HTR.

A method for applying the quantum dot composition QCP on the hole transport region HTR is not particularly limited, and a spin coating method, a casting method, an LB (langmuir-blodgett) method, an inkjet printing method, a Laser Induced Thermal Imaging (LITI) method, or the like may be used. Fig. 8 illustrates the application of the quantum dot composition QCP between the pixel defining films PDL through the nozzle NZ, but the embodiment of the present disclosure is not limited thereto.

The thickness of the emission layer EML is not particularly limited, and may be, for example, about 5nm to about 100nm or about 10nm to about 50 nm.

Fig. 9 is a sectional view schematically illustrating an act (S300) of providing heat to form an emission layer in the method for manufacturing a light emitting element according to the embodiment. According to an embodiment, providing heat to the preliminary emission layer P-EML may be performed by: a heat of about 120 ℃ to about 180 ℃ is supplied to the preliminary emission layer P-EML for 20 minutes or more to induce a reaction in which a portion of the ligand LD bound to the quantum dot QD is removed, and the preliminary emission layer P-EML is cured. That is, the emission layer EML is formed by heating the preliminary emission layer P-EML at about 120 ℃ to about 180 ℃ for 20 minutes or more. When heat is supplied to the preliminary emission layer P-EML, the thermal decomposition auxiliary compound RC absorbs the heat and acts as a radical initiator. The generated radicals react with the radical reactive group RG of the tail TL of the ligand LD to break the bond between the tail TL and the head HD. That is, in the emission layer EML, the quantum dot QD has only the head HD of the ligand LD attached to the surface thereof, and the tail TL of the ligand LD is separated from the head HD and is not attached to the quantum dot QD.

After the formation of the emission layer (S300) in the method for manufacturing a light emitting element according to the embodiment, cleaning of the residue RS (see fig. 10) may be further included (S400). In the cleaning residue RS (S400), some of the residue RS may be removed, and some may remain in the emission layer EML.

Fig. 10 is a cross-sectional view illustrating an emission layer EML manufactured according to an embodiment. In providing heat to the preliminary emission layer P-EML, the ligand LD reacts with the azo compound RC to form the emission layer EML in the form of the surface-modified quantum dots MQD in which the tail TL is removed. Removing a portion of the ligand LD bound to the quantum dots QD allows the distance between the quantum dots QD to be closer. The removed tail TL and the decomposed thermal decomposition assisting compound RC exist as a residue RS, and the residue RS may be removed in a cleaning action, or some may remain in the emission layer EML.

The quantum dot composition according to the embodiments of the present disclosure may exhibit suitable (e.g., excellent) luminous efficiency when applied to a light emitting element, while enhancing the dispersibility and end capping properties of the quantum dot.

The quantum dot having the organic ligand bound to the surface thereof may have improved dispersibility and capping properties in the quantum dot composition, but when applied to a light emitting element, the organic ligand may inhibit charge injection properties, and thus may reduce the light emitting efficiency of the light emitting element. However, the quantum dot composition according to an embodiment of the present disclosure includes a ligand including a radical reactive group and a thermal decomposition auxiliary compound to remove a portion of the ligand bound to the quantum dot when applied to form an emission layer, thereby reducing a distance between the quantum dots. Accordingly, it is possible to achieve an increase in the stacking density of quantum dots, a reduction or prevention of deterioration of charge injection properties, and an improvement in light emission efficiency properties of a light emitting element.

Hereinafter, the present disclosure will be described in more detail by specific examples and comparative examples. The following examples are presented as examples only to aid understanding of the present disclosure, and thus the scope of the present disclosure is not limited thereto.

1. Preparation of exemplaryQuantum dot composition 1

Quantum dot 1 (example compound 1) and azo compound (2,2' - (diazene-1, 2-diyl) bis (2-methylpropanenitrile)) were dispersed in octane at about 1 wt% and about 0.03 wt%, respectively, to prepare examplequantum dot composition 1. In addition, the same method was applied for each of thequantum dots 2 to 13 (example compound 2 to example compound 13) to prepare examplequantum dot compositions 2 to 13, respectively. The quantum dots QD are all the same.

Quantum dots incorporating ligands according to examples

[ example Compound 1]

[ exemplary Compound 2]

[ example Compound 3]

[ exemplary Compound 4]

[ exemplary Compound 5]

[ example Compound 6]

[ exemplary Compound 7]

[ exemplary Compound 8]

[ exemplary Compound 9]

[ example Compound 10]

[ example Compound 11]

[ example Compound 12]

[ exemplary Compound 13]

2. Preparation of comparative exampleQuantum dot composition 1 and comparative exampleQuantum dot composition 2

Thequantum dot 1 of comparative example 1 (comparative compound 1) and thequantum dot 2 of comparative example 2 (comparative compound 2) below were dispersed in octane at about 1 wt% to prepare comparative examplequantum dot composition 1 and comparative examplequantum dot composition 2, respectively. Quantum dots QD are the same as the exemplified quantum dots.

Quantum dots of comparative example

[ comparative Compound 1]

[ comparative Compound 2]

3. Evaluation of dispersed particle diameter and discharge stability of Quantum dot composition

For each of examplequantum dot compositions 1 through 13 and comparative examplequantum dot compositions 1 and 2, the dispersed particle size was measured using ELSZ-2000zs (otsuka). In addition, the discharge stability was evaluated from the adhesion accuracy (e.g., deposition accuracy) from the inkjet head, and for 30 days of discharge, the adhesion accuracy (e.g., deposition accuracy) of ± 5 μm in the x-axis direction and the y-axis direction was evaluated, and when the accuracy was satisfied, it was labeled as spec. The results are shown in table 1 below.

TABLE 1

Referring to table 1, the quantum dot having the ligand bound to the surface thereof according to the example may have desired (e.g., excellent) dispersibility in the quantum dot composition, and thus it was confirmed that the discharge stability was excellent. On the other hand, the comparative examplequantum dot composition 1 has a ligand bonded to a relatively short chain of 2 carbon atoms of the quantum dot, and thus is evaluated to have considerably low dispersion properties in an organic solvent and to have poor discharge stability. The comparative examplequantum dot composition 2 has a ligand of a long chain including 17 carbon atoms bonded to the quantum dot, and thus has excellent dispersibility in an organic solvent and has excellent discharge stability.

4. Evaluation of light-emitting element Properties

1) Manufacture of light-emitting element

The ITO glass substrate (25 mm. times.25 mm, 15. OMEGA/sq (□)) was ultrasonically cleaned using distilled water and isopropyl alcohol in this order, and cleaned with UV ozone for 30 minutes. PEDOT-PSS (Clevios)^TMAI4083) was spin-coated on a clean substrate and baked at 110 ℃ for 30 minutes to form a hole injection layer having a thickness of about 40 nm. A polyvinylcarbazole solution in which polyvinylcarbazole was dissolved in chlorobenzene in an amount of about 1.1 wt% was prepared and spin-coated on the hole injection layer, and then baked in a glove box at 150 ℃ for 30 minutes under a nitrogen atmosphere to form a hole transport layer having a thickness of about 30 nm.

The preliminary emission layer is formed by spin-coating the prepared quantum dot composition (i.e., one of the quantum dot compositions each prepared) on the hole transport layer. Thereafter, baking was performed at 110 ℃ for 30 minutes in a glove box under a nitrogen atmosphere to form an emission layer having a thickness of about 35 nm. Subsequently, a solution in which ZnO nanoparticles were dispersed in ethanol in an amount of about 2.0 wt% was prepared and spin-coated on the emission layer, and then baked in a glove box at 110 ℃ for 30 minutes under a nitrogen atmosphere to form an electron transport layer having a thickness of about 60 nm. On the electron transport layer, aluminum (Al) was deposited to a thickness of about 100nm by thermal evaporation to form a cathode.

2) Evaluation of light-emitting element Properties

The luminance and efficiency of the light emitting element according to each of examples 1 to 13 and comparative examples 1 and 2 were measured, and the results are shown in table 2 below. Power was supplied by a current-voltage meter (Keithley SMU 236) and measurements were performed using a luminance meter PR 650.

TABLE 2

Referring to table 2, it is seen that the light emitting elements of examples 1 to 13 each have a low driving voltage and a desired (e.g., excellent) light emitting efficiency, as compared to the driving voltage and the light emitting efficiency of the light emitting element of each of comparative example 1 and comparative example 2.

The light emitting element of comparative example 1 has an emission layer made of a quantum dot composition having low dispersibility, and thus does not have quantum dots uniformly distributed in the emission layer, thereby having considerably low luminous efficiency.

In the light emitting element of comparative example 2, it was seen that long organic ligands blocking or preventing electron injection remained in the emission layer, and thus the distance between quantum dots was far, and the organic ligands blocked or suppressed electron and hole injection at each interface, thereby reducing the efficiency of the light emitting element.

On the other hand, the light emitting element of each of examples 1 to 13 is manufactured from a quantum dot composition having a desired (e.g., excellent) dispersibility to uniformly distribute quantum dots, and including an azo compound allows effective removal of a tail of a ligand bound to a surface of the quantum dot in the manufacture of an emission layer to reduce a distance between the quantum dots, thereby improving film density to achieve a low driving voltage and improved luminous efficiency.

Referring back to fig. 11 to 13, the display device DD including the light emitting element ED according to the embodiment will be described in more detail.

Fig. 11 is a plan view of a display device DD according to an embodiment. Fig. 12 is a sectional view of the display device DD according to the embodiment corresponding to a line II-II' of fig. 11. Fig. 13 is a sectional view of a display device DD according to an embodiment.

The display device DD of the embodiment may include a plurality of light emitting elements ED-1, ED-2, and ED-3, and the light emitting elements ED-1, ED-2, and ED-3 may include emission layers EML-B, EML-G and EML-R having surface-modified quantum dots MQD1, MQD2, and MQD3, respectively.

In some embodiments, the display device DD may include a display panel DP including a plurality of light emitting elements ED-1, ED-2, and ED-3, and a light control layer PP disposed on the display panel DP. In some embodiments, the optical control layer PP may be omitted from the display device DD of the embodiment, unlike the view shown in the drawings.

The display panel DP may include a base substrate BS, a circuit layer DP-CL, and a display element layer DP-EL disposed on the base substrate BS, and the display element layer DP-EL may include a pixel defining film PDL, light emitting elements ED-1, ED-2, and ED-3 disposed between the pixel defining film PDL (e.g., between portions of the pixel defining film PDL), and an encapsulation layer TFE disposed on the light emitting elements ED-1, ED-2, and ED-3.

Referring to fig. 11 and 12, the display device DD may include a non-light emitting region NPXA and light emitting regions PXA-B, PXA-G and PXA-R. Each of the light emitting regions PXA-B, PXA-G and PXA-R may be a region capable of emitting light generated from each of the light emitting elements ED-1, ED-2, and ED-3. The light emitting areas PXA-B, PXA-G and PXA-R may be spaced apart from each other in a plane.

The light emitting regions PXA-B, PXA-G and PXA-R may be divided into a plurality of groups according to the colors of light generated from the light emitting elements ED-1, ED-2, and ED-3. In the display device DD of the embodiment shown in fig. 11 and 12, three light emitting regions PXA-B, PXA-G and PXA-R that respectively emit (e.g., will emit) blue light, green light, and red light are exemplarily shown. For example, the display device DD of the embodiment may include the blue light emitting region PXA-B, the green light emitting region PXA-G, and the red light emitting region PXA-R separated from each other.

The plurality of light emitting elements ED-1, ED-2, and ED-3 may emit light in different wavelength regions. For example, in an embodiment, the display device DD may include a first light emitting element ED-1 emitting (e.g., to emit) blue light, a second light emitting element ED-2 emitting (e.g., to emit) green light, and a third light emitting element ED-3 emitting (e.g., to emit) red light. However, embodiments of the present disclosure are not limited thereto, and the first, second, and third light emitting elements ED-1, ED-2, and ED-3 may emit light in the same wavelength region or emit light in at least one different wavelength region.

For example, the blue light emitting region PXA-B, the green light emitting region PXA-G, and the red light emitting region PXA-R of the display device DD may correspond to the first light emitting element ED-1, the second light emitting element ED-2, and the third light emitting element ED-3, respectively.

The first emission layer EML-B of the first light emitting element ED-1 may include first surface-modified quantum dots MQD 1. The first surface modified quantum dots MQD1 may emit blue light as the first light.

The second emission layer EML-G of the second light emitting element ED-2 and the third emission layer EML-R of the third light emitting element ED-3 may include second surface-modified quantum dots MQD2 and third surface-modified quantum dots MQD3, respectively. The second surface modified quantum dot MQD2 and the third surface modified quantum dot MQD3 may emit green light as the second light and red light as the third light, respectively.

Each of the first, second, and third surface-modified quantum dots MQD1, MQD2, and MQD3 may have a quantum dot and a head (head of a ligand) bonded to a surface of the quantum dot. The description of the surface-modified quantum dots MQD in the light emitting element of the above embodiment may be equally applied for each of the first, second, and third surface-modified quantum dots MQD1, MQD2, andMQD 3.

In an embodiment, the first quantum dot QD1 of the first surface modified quantum dot MQD1, the second quantum dot QD2 of the second surface modified quantum dot MQD2, and the third quantum dot QD3 of the third surface modified quantum dot MQD3 included in the light emitting elements ED-1, ED-2, and ED-3 may be formed of different core materials. In some embodiments, the first quantum dot QD1 of the first surface modified quantum dot MQD1, the second quantum dot QD2 of the second surface modified quantum dot MQD2, and the third quantum dot QD3 of the third surface modified quantum dot MQD3 may be formed of the same core material, or two quantum dots selected from the first quantum dot QD1, the second quantum dot QD2, and the third quantum dot QD3 may be formed of the same core material, and the rest may be formed of different core materials.

In an embodiment, the first quantum dot QD1 of the first surface modified quantum dot MQD1, the second quantum dot QD2 of the second surface modified quantum dot MQD2, and the third quantum dot QD3 of the third surface modified quantum dot MQD3 may have different diameters. For example, the first quantum dots QD1 used in the first light emitting element ED-1 emitting light in a relatively short wavelength region may have a relatively small average diameter, as compared to the second quantum dots QD2 of the second light emitting element ED-2 and the third quantum dots QD3 of the third light emitting element ED-3, both emitting light in a relatively long wavelength region.

In the present specification, the term "average diameter" refers to an arithmetic average of diameters of a plurality of quantum dot particles. Further, the diameter of the quantum dot particle may be an average value of the width of the quantum dot particle in the cross section.

The relationship of the average diameters of the first, second, and third quantum dots QD1, QD2, and QD3 is not limited to the above limitations. That is, fig. 12 shows that the first, second, and third quantum dots QD1, QD2, and QD3 are similar to each other in size. However, in another embodiment, the first, second, and third quantum dots QD1, QD2, and QD3 included in the light emitting elements ED-1, ED-2, and ED-3 may be different in size. In addition, the average diameters of two quantum dots selected from the first, second, and third quantum dots QD1, QD2, and QD3 may be similar, and the rest may be different.

In embodiments, the first to third ligands of the first, second, and third surface modified quantum dots MQD1, MQD2, and MQD3 may be the same or different from each other. The first to third ligands may be selected accordingly based on the emission wavelengths of the light emitting elements ED-1, ED-2 and ED-3 including the first, second and third surface-modified quantum dots MQD1, MQD2 andMQD 3.

In the display device DD of the embodiment, as shown in fig. 11 and 12, the areas of each of the light emitting regions PXA-B, PXA-G and PXA-R may be different from each other. In this case, the term "area" may refer to an area when viewed on a plane defined by the first direction DR1 and thesecond direction DR 2.

The light emitting regions PXA-B, PXA-G and PXA-R may have different areas according to colors of light emitted from the emission layers EML-B, EML-G and EML-R of the light emitting elements ED-1, ED-2 and ED-3. For example, referring to fig. 11 and 12, in the display device DD of the embodiment, the blue light emitting region PXA-B corresponding to the first light emitting element ED-1 emitting blue light may have the largest area, and the green light emitting region PXA-G corresponding to the second light emitting element ED-2 generating green light may have the smallest area. However, embodiments of the present disclosure are not limited thereto, and the light emitting regions PXA-B, PXA-G and PXA-R may emit light other than blue, green, and red light, or the light emitting regions PXA-B, PXA-G and PXA-R may each have the same area, or the light emitting regions PXA-B, PXA-G and PXA-R may be disposed at area ratios different from those shown in fig. 11.

Each of the light emitting regions PXA-B, PXA-G and PXA-R may be regions separated by a pixel defining film (or pixel defining layer) PDL. The non-light emitting region NPXA may be a region between adjacent light emitting regions PXA-B, PXA-G and PXA-R, and may correspond to the pixel defining film PDL. On the other hand, in the present specification, each of the light emitting regions PXA-B, PXA-G and PXA-R may correspond to a pixel. The pixel defining film PDL may partition the light emitting elements ED-1, ED-2, and ED-3. The emission layers EML-B, EML-G and EML-R of the light emitting elements ED-1, ED-2, and ED-3 may be disposed in the openings OH defined by the pixel defining film PDL and spaced apart in the openings OH defined by the pixel defining film PDL.

The pixel defining film PDL may be formed of a polymer resin. For example, the pixel defining film PDL may be formed to include a polyacrylate type resin or a polyimide type resin. In addition, the pixel defining film PDL may be formed by including an inorganic material in addition to the polymer resin. In some embodiments, the pixel defining film PDL may be formed to include a light absorbing material, or may be formed to include a black pigment or a black dye. The formed pixel defining film PDL including the black pigment or the black dye may realize a black pixel defining film. When the pixel defining film PDL is formed, carbon black may be used as a black pigment or a black dye, but the embodiment of the present disclosure is not limited thereto.

In some embodiments, the pixel defining film PDL may be formed of an inorganic material. For example, the pixel defining film PDL may be formed including silicon nitride (SiN)_x) Silicon oxide (SiO)_x) Silicon oxynitride (SiO)_xN_y) And the like. The pixel defining film PDL may define the light emitting regions PXA-B, PXA-G and PXA-R. The light emitting regions PXA-B, PXA-G and PXA-R and the non-light emitting region NPXA may be separated by the pixel defining film PDL.

Each of the light emitting elements ED-1, ED-2, and ED-3 may include a first electrode EL1, a hole transport region HTR, one or more emission layers EML-B, EML-G and EML-R, an electron transport region ETR, and asecond electrode EL 2. The description in connection with fig. 4 may be equally applied to the first electrode EL1, the hole transport region HTR, the electron transport region ETR, and the second electrode EL2 except that the first surface-modified quantum dot MQD1, the second surface-modified quantum dot MQD2, and the third surface-modified quantum dot MQD3 included in the emission layers EML-B, EML-G and EML-R are different from each other in the light emitting elements ED-1, ED-2, and ED-3 included in the display device DD of the embodiment. In some embodiments, each of the light emitting elements ED-1, ED-2, and ED-3 may further include a cap layer between the second electrode EL2 and the encapsulation layer TFE.

The encapsulation layer TFE may cover the light emitting elements ED-1, ED-2, and ED-3. The encapsulation layer TFE may be a single layer or a laminate comprising a plurality of layers. The encapsulation layer TFE may be a thin film encapsulation layer. The encapsulation layer TFE protects the light emitting elements ED-1, ED-2, and ED-3. The encapsulation layer TFE may cover the upper surface of the second electrode EL2 disposed in the opening OH, and may fill the opening OH.

In fig. 12, the hole transport region HTR and the electron transport region ETR are illustrated as a common layer covering the pixel defining film PDL, but embodiments of the present disclosure are not limited thereto. In an embodiment, the hole transport region HTR and the electron transport region ETR may be disposed (e.g., only disposed) in the opening OH defined by the pixel defining film PDL.

For example, when the hole transport region HTR and the electron transport region ETR other than the emission layers EML-B, EML-G and EML-R are provided by the inkjet printing method, the hole transport region HTR, the emission layers EML-B, EML-G and EML-R, the electron transport region ETR, and the like may be disposed to correspond to the opening OH defined between the pixel defining layers PDL. However, embodiments of the present disclosure are not limited thereto, and as shown in fig. 13, the hole transport region HTR and the electron transport region ETR may cover the pixel defining layer PDL without being patterned, and may be provided as one common layer regardless of a method of providing each functional layer.

In the display device DD of the embodiment shown in fig. 12, although the thicknesses of the emission layers EML-B, EML-G and EML-R of the first, second, and third light emitting elements ED-1, ED-2, and ED-3 are shown to be similar to each other, embodiments of the present disclosure are not limited thereto. For example, in the embodiment, the thicknesses of the emission layers EML-B, EML-G and EML-R of the first, second, and third light emitting elements ED-1, ED-2, and ED-3 may be different from each other.

Referring to fig. 11, blue light-emitting areas PXA-B and red light-emitting areas PXA-R may be alternately arranged in the first direction DR1 to form afirst group PXG 1. The green light emitting areas PXA-G may be arranged in the first direction DR1 to form asecond group PXG 2.

The first and second sets ofPXGs 1 and 2 may be spaced apart from each other in thesecond direction DR 2. Each of the first and second sets ofPXGs 1 and 2 may be provided in plurality. The first and second sets ofPXGs 1 and 2 may be alternately arranged in thesecond direction DR 2.

One green light-emitting region PXA-G may be disposed to be spaced apart from one blue light-emitting region PXA-B or one red light-emitting region PXA-R in the fourth direction DR 4. The fourth direction DR4 may be a direction between the first direction DR1 and thesecond direction DR 2.

The arrangement structure of the light emitting areas PXA-B, PXA-G and PXA-R shown in FIG. 11 may have

Structure or pattern (

Is a registered trademark owned by Samsung Display co, Ltd). However, the arrangement structure of the light emitting regions PXA-B, PXA-G and PXA-R in the display device DD according to the embodiment is not limited to the arrangement structure shown in fig. 11. For example, in an embodiment, the light-emitting regions PXA-B, PXA-G and PXA-R may have a stripe structure in which the blue light-emitting regions PXA-B, the green light-emitting regions PXA-G, and the red light-emitting regions PXA-R may be alternately arranged along thefirst direction DR 1.

Referring to fig. 12, the display device DD of the embodiment further includes an optical control layer PP. The optical control layer PP may block external light incident to the display panel DP from the outside of the display device DD. The light control layer PP may block a portion of external light. The optical control layer PP may perform a reflection reducing or preventing function to reduce or minimize reflection due to external light.

In the embodiment shown in fig. 12, the optical control layer PP may include a color filter layer CFL. That is, the display device DD of the embodiment may further include a color filter layer CFL disposed on the light emitting elements ED-1, ED-2, and ED-3 of the display panel DP.

In the display device DD of the embodiment, the optical control layer PP may include a base layer BL and a color filter layer CFL.

The base layer BL may be a member that provides a surface of the base on which the color filter layer CFL is disposed. The base layer BL may be a glass substrate, a metal substrate, a plastic substrate, or the like. However, embodiments of the present disclosure are not limited thereto, and the base layer BL may be an inorganic layer, an organic layer, or a composite material layer.

The color filter layer CFL may include a light blocking unit BM and a color filter CF. The color filter CF may include a plurality of filters CF-B, CF-G and CF-R. That is, the color filter layer CFL may include a first filter CF-B transmitting the first color light, a second filter CF-G transmitting the second color light, and a third filter CF-R transmitting the third color light. For example, the first filter CF-B may be a blue filter (e.g., a blue filter), the second filter CF-G may be a green filter (e.g., a green filter), and the third filter CF-R may be a red filter (e.g., a red filter).

Each of the filters CF-B, CF-G and CF-R may include a polymeric photosensitive resin and a pigment and/or dye. The first filter CF-B may include blue pigments and/or blue dyes, the second filter CF-G may include green pigments and/or green dyes, and the third filter CF-R may include red pigments and/or red dyes.

However, embodiments of the present disclosure are not limited thereto, and the first filter CF-B may not include any pigment or dye. The first filter CF-B may include a polymer photosensitive resin, but may not include a pigment or dye. The first filter CF-B may be transparent. The first filter CF-B may be formed of a transparent photosensitive resin.

The light blocking unit BM may be a black matrix. The light blocking unit BM may be formed to include an organic light blocking material and/or an inorganic light blocking material each including a black pigment and/or a black dye. The light blocking unit BM may reduce or prevent light leakage and separate the boundaries between adjacent filters CF-B, CF-G and CF-R.

The color filter layer CFL may further include a buffer layer BFL. For example, buffer layer BFL may be a protective layer that protects filters CF-B, CF-G and CF-R. The buffer layer BFL may be an inorganic material layer including at least one inorganic material selected from silicon nitride, silicon oxide, and silicon oxynitride. The buffer layer BFL may be formed of a single layer or a plurality of layers.

In the embodiment shown in fig. 12, the first filter CF-B of the color filter layer CFL is shown to overlap the second filter CF-G and the third filter CF-R, but embodiments of the present disclosure are not limited thereto. For example, the first filter CF-B, the second filter CF-G, and the third filter CF-R may be separated by the light blocking unit BM and may not overlap each other. In some embodiments, each of the first filter CF-B, the second filter CF-G, and the third filter CF-R may be disposed corresponding to each of the blue light-emitting area PXA-B, the green light-emitting area PXA-G, and the red light-emitting area PXA-R.

Unlike those shown in fig. 12 and the like, the display device DD of the embodiment may include a polarizing layer as the light control layer PP instead of the color filter layer CFL. The polarizing layer may block external light supplied from the outside to the display panel DP. The polarizing layer may block a portion of external light.

In addition, the polarizing layer may reduce reflected light generated in the display panel DP by external light. For example, the polarizing layer may function to block reflected light in a case where light provided from the outside of the display device DD is incident to the display panel DP and re-emitted. The polarizing layer may be a circular polarizer having a reflection reducing or preventing function, or the polarizing layer may include a linear polarizer and a λ/4 phase retarder. In some embodiments, the polarizing layer may be disposed on the base layer BL to be exposed, or the polarizing layer may be disposed under the base layer BL.

Fig. 13 is a sectional view of a display device DD-1 of another embodiment of the present disclosure. In the description of the display device DD-1 according to the embodiment, contents overlapping with those described above with reference to fig. 1 to 12 will not be described again, and only differences will be mainly described.

Referring to fig. 13, the display device DD-1 of the embodiment may include a light conversion layer CCL disposed on the display panel DP-1. In some embodiments, the display device DD-1 may further include a color filter layer CFL. The color filter layer CFL may be disposed between the base layer BL and the light conversion layer CCL.

The display panel DP-1 may be a light emitting display panel. For example, the display panel DP-1 may be an organic electroluminescent display panel or a quantum dot light emitting display panel.

The display panel DP-1 may include a base substrate BS, a circuit layer DP-CL disposed on the base substrate BS, and a display element layer DP-EL 1.

The display element layer DP-EL1 includes a light emitting element ED-a, and the light emitting element ED-a may include a first electrode EL1 and a second electrode EL2 facing each other and a plurality of layers OL disposed between the first electrode EL1 and thesecond electrode EL 2. The plurality of layers OL may include a hole transport region HTR (fig. 4), an emission layer EML (fig. 4), and an electron transport region ETR (fig. 4). The encapsulation layer TFE may be disposed on the light emitting element ED-a.

In the light emitting element ED-a, the same contents as those described with reference to fig. 4 may be applied to the first electrode EL1, the hole transporting region HTR, the electron transporting region ETR, and thesecond electrode EL 2. However, in the light emitting element ED-a included in the display panel DP-1 of the embodiment, the emission layer may include a host and a dopant as an organic electroluminescent material, or may include surface-modified quantum dots described with reference to fig. 1 to 12. In the display panel DP-1 of the embodiment, the light emitting element ED-a may emit blue light.

The light-converting layer CCL may include a plurality of partition walls BK disposed spaced apart from each other, and light control units CCP-B, CCP-G and CCP-R disposed between the partition walls BK. The partition wall BK may be formed of a composition including a polymer resin and a coloring additive. The partition wall BK may be formed to include a light absorbing material, or to include a pigment and/or a dye. For example, the partition wall BK may include a black pigment or a black dye to realize a black partition wall. When the black partition walls are formed, carbon black or the like may be used as the black pigment and/or the black dye, but embodiments of the present disclosure are not limited thereto.

The light conversion layer CCL may include a first light control unit CCP-B that transmits the first light, a second light control unit CCP-G that includes fourth surface modified quantum dots MQD2-a to convert the first light to the second light, and a third light control unit CCP-R that includes fifth surface modified quantum dots MQD3-a to convert the first light to the third light. The second light may be light of a longer wavelength region than that of the first light, and the third light may be light of a longer wavelength region than that of the first and second lights. For example, the first light may be blue light, the second light may be green light, and the third light may be red light. With respect to the surface-modified quantum dots, MQD2-a and MQD3-a, included in the light control units CCP-G and CCP-R, the same contents as those of the surface-modified quantum dots used in the emission layer shown in FIG. 12 can be applied.

The light conversion layer CCL may further include a cap layer CPL. The cover layer CPL may be disposed on the light control units CCP-B, CCP-G and CCP-R and the partition wall BK. The cap layer CPL may serve to reduce or prevent the permeation of moisture and/or oxygen (hereinafter, referred to as "moisture/oxygen"). The cap layer CPL may be disposed over the light control units CCP-B, CCP-G and CCP-R to reduce or prevent exposure of the light control units CCP-B, CCP-G and CCP-R to moisture/oxygen. The cap layer CPL may comprise at least one inorganic layer.

The display device DD-1 of the embodiment may include the color filter layer CFL disposed on the light conversion layer CCL, and the description of fig. 12 may be equally applied to the color filter layer CFL and the base layer BL.

The quantum dot composition of the embodiment may be used as an emission layer material capable of exhibiting improved light emission efficiency properties by binding ligands, which may be removed, to the surface of the quantum dot to reduce or prevent deterioration of electron injection properties even when applied to the emission layer.

The light emitting element and the display device of the embodiments include quantum dots in an emission layer and may exhibit improved luminous efficiency and lifespan without deteriorating electron injection properties.

When describing embodiments of the present invention, the use of "may (may)" refers to "one or more embodiments of the present invention. Moreover, the term "exemplary" is intended to mean exemplary or illustrative.

As used herein, the terms "substantially", "about" and the like are used as approximate terms and not as degree terms, and are intended to account for inherent deviations in measured or calculated values that would be recognized by one of ordinary skill in the art. Moreover, any numerical range recited herein is intended to include all sub-ranges of equal numerical precision encompassed within the recited range. For example, a range of "1.0 to 10.0" is intended to include all sub-ranges between (and including) the recited minimum value of 1.0 and the recited maximum value of 10.0 (and including the recited minimum value of 1.0 and the recited maximum value of 10.0), i.e., having a minimum value equal to or greater than 1.0 and a maximum value of equal to or less than 10.0, such as, for example, 2.4 to 7.6. Any maximum numerical limitation recited herein is intended to include all smaller numerical limitations contained therein, and any minimum numerical limitation recited herein is intended to include all larger numerical limitations contained therein. Accordingly, applicants reserve the right to modify the specification (including the claims) to expressly state any sub-ranges subsumed within the ranges expressly stated herein. It is intended in this specification to inherently describe all such ranges so modifications as to explicitly state any such subranges would be desirable.

While the present disclosure has been described with reference to the exemplary embodiments thereof, it will be understood that the present disclosure should not be limited to these embodiments but various changes and modifications can be made by one skilled in the art without departing from the spirit and scope of the present disclosure.

Therefore, the technical scope of the present disclosure is not intended to be limited to the contents set forth in the detailed description of the specification, but is intended to be defined by the appended claims and equivalents thereof.

Claims (17)

1. A quantum dot composition, the quantum dot composition comprising:

a quantum dot having a surface to which a ligand is bound; and

thermally decomposing the auxiliary compound.

2. The quantum dot composition of claim 1, wherein the ligand comprises:

a head bonded to the surface of the quantum dot; and

a tail comprising at least one free radical reactive group.

3. The quantum dot composition of claim 2, wherein the free radical reactive group is a carbonyl group, an ester group, an ether group, a peroxy group, an azo group, a carbamate group, a thiocarbamate group, a carbonate group, or a xanthate group.

4. The quantum dot composition of claim 1, wherein the ligand is a monodentate ligand or a bidentate ligand.

5. The quantum dot composition of claim 2, wherein the head comprises a thiol group, a hydroxyl group, a phosphine group, a fluorenyl group, an amine group, or a carboxylic acid group.

6. The quantum dot composition of claim 5, wherein the head further comprises an alkyl group having 1 to 6 carbon atoms.

7. The quantum dot composition of claim 2, wherein the tail is represented by any one selected from formula 1 to formula 6:

formula 1

Formula 2

Formula 3

Formula 4

Formula 5

Formula 6

Wherein, in the formulae 1 to 6,

R₂is an alkyl group having 2 to 20 carbon atoms,

m is an integer of 1 to 5, and

"+" indicates the position of attachment to the head.

8. The quantum dot composition of claim 2, wherein the thermal decomposition assisting compound is an azo compound.

9. The quantum dot composition of claim 8, wherein the azo compound is represented by formula 7:

formula 7

Ra-N＝N-Rb，

Wherein, in the formula 7,

ra and Rb are each independently an alkyl group having 2 to 20 carbon atoms.

10. The quantum dot composition of claim 1, wherein the amount of the quantum dots having the ligand bound to the surface of the quantum dots is 0.5 wt% to 10 wt% relative to the total amount of the quantum dot composition.

11. The quantum dot composition according to claim 1, wherein the amount of the thermolysis assistance compound is 0.01 to 1 wt% with respect to the total amount of the quantum dot composition.

12. The quantum dot composition of claim 1,

wherein the quantum dot composition further comprises an organic solvent, and

wherein the quantum dots are dispersed in the organic solvent.

13. The quantum dot composition of claim 1, wherein the quantum dot is a semiconductor nanocrystal comprising a core and a shell surrounding the core.

14. A method for manufacturing a light emitting element, the method comprising the steps of:

forming a hole transport region on the first electrode;

forming an emission layer on the hole transport region;

forming an electron transport region on the emission layer; and

forming a second electrode on the electron transport region,

wherein the step of forming the emission layer comprises: dispersing a quantum dot having a surface to which a ligand is bonded and a thermal decomposition auxiliary compound in an organic solvent to prepare a quantum dot composition; applying the quantum dot composition on the hole transport region to form a preliminary emission layer; and heating the preliminary emission layer.

15. The method of claim 14, wherein heating the preliminary emissive layer comprises heating the preliminary emissive layer at 120 ℃ to 180 ℃ for 20 minutes or more.

16. A light emitting element, comprising:

a first electrode;

a hole transport region on the first electrode;

an emissive layer located on the hole transport region;

an electron transport region on the emission layer; and

a second electrode on the electron transport region,

wherein the emission layer includes quantum dots having a surface to which hydrophilic groups are bonded.

17. The light-emitting element according to claim 16, wherein the emission layer further comprises a residue containing a radical reactive group.

Images